The screw spindle pump is a so-called displacement pump, wherein the form of the rotating displacer resembles that of a spindle screw. The screw spindle pump comprises two or more contrarotating rotors and a pump housing which encloses the rotors. The rotors are constituted with a regular threaded profiling and engage with one another in a cogwheel-like manner. The rotors are also referred to as screw spindles and comprise at least a first shank section and a profiled section with a screw-like or helical profile. The hollow spaces, which are formed by the at least three structural elements—pump housing, first screw spindle and at least second screw spindle, form the delivery spaces for the delivered medium. When the screw spindles are rotated, the delivery spaces move in a machine direction and deliver the medium inside the pump housing from the suction side (=inlet channel) to the pressure side (=outlet channel).
This type of pump is particularly well suited for incompressible as well as viscous media and for generating high pressures. Screw spindle pumps are used for the transport of single-phase as well as multi-phase fluids. The three-spindle screw spindle pump is used predominantly for pumping lubricants that are free of abrasive materials. They are characterised in particular by the fact that it is possible to generate high pressures up to 160 bar with them.
In the case of three-spindle screw spindle pumps, the three spindles are usually disposed in such a way that a drive spindle lying in the middle (also referred to as the male screw) drives two laterally engaging female screw spindles. The drive spindle, for its part, is connected to a drive motor, which can be constituted both as an electric motor and as an internal combustion engine. The torque generated by the drive is transmitted from the drive spindle via the spindle profile to the driven spindles. The spindle profiles engaging with one another produce closed delivery chambers, in which the delivery medium is enclosed and transported in the axial direction from the suction side to the pressure side.
In order to reduce the loads acting on the male screw, the female screws are positioned, proceeding from the rotational axis of the male screw, at an angle of 180° in the pump housing, which balances out the radial force effect on the male screw. The female screws are mounted hydraulically, in that the pump delivery medium is pressed under pressure and motion into the small gap between the screws and the pump housing and thus builds up the carrier film, which in turn prevents tarnishing of the spindles. Housing denotes the part of the pump in which all three spindles are embedded. The delivery chambers are sealed off at the external diameter of the respective pump spindle on the housing.
The problem of the invention is to optimise the flow of the transported medium in the pump, in particular in the region of the outlet channel. Moreover, the formation of eddies which disrupt the transport and lead to flow losses are reduced in this region.
The above problem is solved by a screw spindle pump and a method for operating a screw spindle pump which has the features in claims 1 and 12. Further advantageous embodiments are described in the sub-claims.